DIE SWELL OF LIQUID CRYSTAL-FORMING SOLUTIONS OF HYDROXYPROPYL CELLULOSE THROUGH A LONG CAPILLARY DIE

The die swell and shear viscosity of lyotropic liquid crystal-forming hydroxypropyl cellulose solutions in N,N-dimethylacetamide were determ ined over a relatively wide range of shear stress or polymer concentra tion at 30 degrees C by using a long capillary die with an aspect rati o of 114. The dependence of die swell on the concentration was similar to that of shear viscosity: a maximum at a critical concentration C-a and a minimum at another critical concentration C-b (C-a < C-b). The dependence of the swell on shear stress is greatly affected by the sol ution phase: in an isotropic range (below C-a), the die swell increase d monotonously with shear; in the vicinity of C-a, the die swell exhib ited a maximum; in a biphasic range (between C-a and C-b), the die swe ll decreased monotonously; in a single-phase anisotropic range (above C-b), the die swell exhibited a minimum. Above C-b, extrudate distorti on was observed and disappeared around the shear where the die swell e xhibited a minimum.